A number of properties of a neuron change in a coordinated fashion to store a given type of memory. Our long- term goal is to determine which properties of neurons change, and how these properties are regulated during formation of memories. Regulation of glutamate transporter activity may be necessary during increases in synaptic efficacy to maintain the fidelity of synaptic transmission and to avoid toxicity that might occur if glutamate is elevated in the synaptic cleft for too long. Thus, we hypothesize that increases in glutamate transporter activity will accompany increases in synaptic efficacy at glutamatergic synapses, especially ones involving long-term changes in synaptic efficacy. This hypothesis will be tested in vitro by investigating regulation of glutamate uptake after induction of LTP and in vivo by investigating regulation of glutamate uptake after contextual fear conditioning. Area CA1 of the rat hippocampus will be used in most experiments. We will use a multidisciplinary approach including electrophysiology, biochemistry and behavioral analysis to investigate the regulation of glutamate uptake. The proposed research has four specific aims. Most of the experiments in Specific Aims 1-3 will investigate regulation of glutamate transport during two different forms of LTP (E- and L-LTP). Aim 1 is to characterize the mechanisms involved in the increase in glutamate uptake produced by high frequency stimulation. Aim 2 is to determine whether induction of LTP increases the expression of glutamate transporters, and what mechanisms are involved in the increase in expression. Aim 3 is to investigate the relationship between LTP and changes in glutamate uptake and expression of glutamate transporters. Aim 4 is to determine whether an associative learning paradigm, contextual fear conditioning, produces an increase in glutamate transport in the hippocampus in vivo. In our lab, recent studies have shown that glutamate uptake is regulated during long-term memory in Aplysia, and preliminary results indicate that glutamate uptake is regulated during LTP in the rat hippocampus as well. Thus, the results of these studies will likely indicate that regulation of glutamate transport is a general phenomenon at glutamatergic synapses involved in synaptic plasticity. As glutamate is a remarkably potent and rapidly acting neurotoxin, fundamental studies of long-term regulation of glutamate transport should aid solutions to brain trauma and diseases such as amyotrophic lateral sclerosis.